Note: Descriptions are shown in the official language in which they were submitted.
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
ANTI-LOADING TREATMENTS
BACKGROUND OF THE INVENTION
Coated abrasive products are used to sand a wide variety of substrates,
which can include soft, difficult to finish materials, such as painted
surfaces. When
finishing these soft materials the coated abrasive products cannot perform to
their
maximum potential because of premature loading. Loading is the coalescence of
swans which clog the spaces between abrasive grains, thus preventing the
abrasive
product from being able to continue to effectively abrade the work substrate
or
surFace. The abrasives industry approach is to utilize chemical compounds,
such
as metal soaps (i.e., zinc stearates, calcium stearates) applied as an
oversize
coating, or incorporated into the size coat, which is typically referred to as
the first
sizing coating. Stearate technology provides adequate stock removal and anti-
loading characteristics. However, metal stearates leave a residue of low
surface
energy material on the work surface, that can potentially cause post-
processing
problems, such as coating defects in down stream painting processes.
Contamination of this low surface energy material can be detected by
measuring the water contact angle on the sanded substrate. The typical
practice
to address this issue is to clean the sanded surface with solvent wipes to
insure that
preferably all the contamination is removed, or finish with a non-stearated
product.
SUMMARY OF THE INVENTION
It would be preferable to eliminate the step of cleaning the sanded surface
with solvent wipes, which expends valuable time. and money in the painting
process.
Further, non-stearated products generally do not provide long life.
In one embodiment, an abrasive, such as coated or composite abrasive, is
oversized with a layer consisting essentially of an inorganic, anti-loading
agent
selected from the group consisting of metal silicates, silicas, metal
carbonates, and
metal sulfates.
The layer consists essentially of the inorganic anti-loading additive and this
is meant to indicate that the layer comprises no additive having organic
components
such as typify conventional anti-loading additives, including metal salts of
organic
acids, organophosphate, organosilicates, organoborates and the like. It does
not
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
however preclude the presence of a cured binder component that provides the
vehicle by which the inorganic loading agent is applied.
The metal silicates can be selected from the group consisting of magnesium
silicates, potassium aluminum silicates, aluminum silicates, and calcium
silicates.
In one embodiment, the magnesium silicates include talc, the potassium
aluminum
silicates include micas, the aluminum silicates include clays, and the calcium
silicates include wollastonite. The silicas can be selected from the group
consisting
of fused silica, fumed silica, and precipitated amorphous silica. The metal
carbonates can include calcium carbonate. The metal sulfates can include
hydrous
calcium sulfate or anhydrous calcium sulfate.
The anti-loading agent can have a Mohs hardness value of less than about
7, and preferably less than about 3. The anti-loading agent can have a mean
particle diameter size of less than about 30 micrometers and preferably in the
range
of between about 1 and about 20 micrometers. This allows the anti-loading
agent
to form sufficiently small particles that combine with swarf from a sanded
surface,
such as a painted metal surface, to prevent sufficient agglomerating loading
of swarf
in a surface of the coated abrasive. That is, the particles of the anti-
loading agent
are of such a size that, upon sanding a painted surface using the coated
abrasive
to produce abraded swarf, particles of the anti-loading agent are released
that
?0 combine with and inhibit the agglomeration of such swarf particles.
In a further embodiment, the concentration of the anti-loading agent is
concentrated predominantly in the oversized layer. For example, the
concentration
can be at least 10 percent, by volume, and preferably at least about 60
percent, by
volume, of the oversized layer.
The anti-loading agent is preferably dispersed in a binder, for example,
comprising a thermoplastic or thermoset resin. For example, the thermoplastic
resin
can include latex and the thermoset resin can be selected from the group
consisting
of urea formaldehyde, phenolic, epoxy, urethane, and radiation curable resin
systems.
An abrasive, such as a coated or composite abrasive, is also provided which
includes a backing layer having a first surface, an abrasive layer having a
plurality
-2-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
of abrasive particles disposed on the first surface of the backing layer, and
a layer
consisting essentially of an inorganic anti-loading agent disposed over the
abrasive
layer. In one embodiment, the anti-loading agent is deposited on a cured size
coat.
A method for forming an abrasive, such as a coated or composite abrasive,
is also provided which includes attaching a plurality of abrasive particles to
a first
surface of a backing layer and depositing a layer consisting essentially of an
anti-
loading agent over the abrasive particles.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the invention
will be apparent from the following more particular description of preferred
embodiments of the invention. The accompanying drawing is not necessarily to
scale, emphasis instead being placed upon illustrating the principles of the
invention.
The Figure illustrates a contact angle 8 given a solid, liquid, and vapor.
DETAILED DESCRIPTION OF THE INVENTION
Coated abrasives generally comprise those products having abrasive grits
adhered to a support backing which can be used to abrade or otherwise wear
down
a surface of an article to which they are applied.
The support backing of a coated abrasive may be rigid, but generally is
flexible and typically comprises a web of material, such as paper, cloth,
fibrous pad,
polymeric film, vulcanized fiber, or a combination of such materials and the
like. In
some applications, the support backing initially includes a collection of
loose fibers,
to which the abrasive grits are added, with or without further binder
material, to
provide an abrasive web having grits throughout. The loose collection of
fibers and
grits may be compressed, if no adhering binder is present, or otherwise fixed
or
cured when a binder is present to form the coated abrasive.
The abrasive grits can generally be any material which has the capability of
abrading the workpiece article and typically includes sand, flint, corundum,
metallic
oxides such as aluminum oxide, aluminum-zirconia, ceramic alumina, diamond,
-3-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
silicon carbide, garnet, rouge, crocus, and the like. The grits typically have
sharp
edges which act as the abrading means, but the quality and quantity of the
sharp
edges depends upon the utility. The grits can be embedded into or intermingled
with the support backing, but, more typically are adhered to the support
backing by
an appropriate binder material. The grits can be applied or intermingled with
the
web in a specific pattern or grain or may be randomly distributed. Typically
elaborate measures are taken to assure that the coated abrasive 'has a fixed
grain
with an appropriate distribution of granular cutting edges in one or more
layers.
The binder material is generally any convenient material which can act to
adhere the grits to the support backing and have resistance to negating the
abrading
process. Typical binder materials include the phenolic resins, hide glues,
varnishes,
epoxy resins, acrylates, multi-functional acrylates, urea-formaldehyde resins,
trifunctional urethanes, polyurethane resins, lacquers, enamels and any of a
wide
variety of other materials which have the ability to stabilize the grits in
adhering
relationship to the support backing. Generally, the binding material is
carefully
chosen to provide maximum efficiency of the coated abrasive for the abrading
surface contemplated. Care is taken in selecting binder materials which can
resist
softening or burning or both due to overheating yet provide adequate
adherency.
The grits can be sprayed or otherwise coated with the binder material and
deposited on or about the support backing, or the support backing may be
coated
with the binder material and the grits thereafter deposited thereon. Many
alternate
forms of support backings, granular materials, binder materials, means of
arranging
the grits on the support backing, means of adhering the grits and the like are
known
in the prior art and are seen as variation contemplated as within the scope of
this
invention.
Generally in the manufacture of a conventional coated abrasive, a backing,
(with or without a pre-treatment), is given a maker coat of a binder resin is
applied
and, while the resin is still tacky, abrasive grits are applied over the maker
coat, and
the binder is cured so as to hold the grits in place. A size coat, comprising
essentially a binder resin and optionally fillers, grinding aids and the like,
is then
applied over the grits and cured. The primary function of the size coat is to
anchor
-4-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
the grits in place and allow them to abrade a workpiece without being pulled
from
the coated abrasive structure before their grinding capability had been
exhausted.
In some cases, a supersize layer is deposited over the size coat. The function
of
this layer is to place on the surface of the coated abrasive an additive that
provides
a special characteristic, such as enhanced grinding capability, surface
lubrication,
anti-static properties or, in this case, anti-loading properties. The
supersize layer
generally, but not necessarily, plays no part in securing the grits in place
on the
coated abrasive.
The additive may be applied as a dispersion in a binder (which will be
subsequently cured), or in a liquid dispersion which will simply dry leaving
the
additive on the surface. In one embodiment, the binder includes a
thermoplastic or
thermoset resin. For example, the thermoplastic resin can include latex and
the
thermoset resin can be selected from the group consisting of urea
formaldehyde,
phenolic, epoxy, urethane, and radiation curable resin systems. With some
additives, adhesion to the surface can be achieved without the need for a
dispersion
medium.
In accordance with the present invention, the anti-loading agents, which are
applied over the size coating, can be selected from the group consisting of
metal
silicates, silicas, metal carbonates, and metal sulfates. The metal silicates
can be
selected from the group consisting of magnesium silicates, potassium aluminum
silicates, aluminum silicates, and calcium silicates. In one embodiment, the
magnesium silicates include talc, the potassium aluminum silicates include
micas,
the aluminum silicates include clays, and the calcium silicates include
wollastonite.
The silicas can be selected from the group consisting of fused silica, fumed
silica,
?5 and precipitated amorphous silica. The metal carbonates can include calcium
carbonate. The metal sulfates can include hydrous calcium sulfate or anhydrous
calcium sulfate.
In accordance with the present invention, the inorganic anti-loading agent, in
the course of use, appears to release fine particles that coat fine swarf
particles
generated by the grinding process thus preventing them form agglomerating to
form
troublesome larger particles that get trapped on the coated abrasive surface,
(known
-5-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
as "loading"), reducing its effectiveness. Thus loading of the coated abrasive
is
reduced without causing the problems associated with the use of the
conventional
stearated anti-loading layers. With such additives, a fine coat of low energy
material
is smeared on the abraded surface which makes subsequent painting or polishing
of the surface very difficult unless this coat is removed.
The anti-loading agent of the present invention, in one embodiment, is
relatively soft, for example, having a Mohs hardness value of less than about
7, and
preferably less than about 3. In one embodiment, the loading agent has a mean
particle diameter size range of less than about 30 micrometers and preferably
7 0 between about 1 and about 20 micrometers as finer particles size materials
appear
to function better as an anti-loading agent.
It is believed that one mechanism for providing a non-loading characteristic
is for the anti-loading agent to prevent the swarf particles from adhering to
each
other, therefore reducing loading. This approach produces fine dust during
sanding,
while without the inorganic anti-loading agent, the swarf tends to form balls
or large
chips which become lodged in between the grain particles, which prevent
effective
grinding, and reduce the life of the coated abrasive. The difference in the
appearance of the swarf resulted from sanding with stearated and non-stearated
products are visible.
In accordance with the present invention, the concentration of the anti-
loading
agent in a sanding surface of the oversized layer is greater than about 10
percent,
by volume, and preferably greater than about 60 percent. This assures the anti-
loading agent is sufficiently present to be effective to produce the find dust
which
prevents the swarf from agglomerating.
?5 The anti-loading agent can be used with other abrasives, such as composite
(non-woven) abrasives.
Example 1: Hydrous Magnesium Silicate (Talc) in different median particle
sizes
In the following Example and those following a standard conventional coated
abrasive is used. The backing material is an A-weight paper and the make coat
and
-6-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
size coat comprise a urea-formaldehyde binder. In each case the abrasive
particles
are P320 aluminum oxide. To this base coated abrasive, an oversize coat is
applied
comprising an anti-load additive. In one case, no additive was applied for
comparative purposes. In a second case, an oversize coating containing zinc
stearate is applied and in three other cases the applied coating was hydrous
magnesium silicate (talc) with different particle size. The additives were
applied as
dispersion in latex and water.
The coated abrasives were then used to abrade an acrylic panel using a dual
action sander for six contacts of two minute interval each. The grinding was
done
by a 12.7 cm (5-inch) disc with a 4.5 kg (10-Ib.) load. The amount of cut
after the
total grinding time of 12 minutes was recorded, and the grinding performance
was
measured as percent cut of the control. The average surface roughness values,
Ra
(the arithmetic average of roughness) were also measured. The results are
recorded in the Table 1 below which demonstrates that talc is as effective as
the
more conventional zinc stearate.
-7-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
Anti-load None Zinc Hydrous Hydrous Hydrous
Material Stearate Magnesium Magnesium Magnesium
Silicate Silicate Silicate
(Talc) (Talc) (Talc)
Item Base Zinc Vertal Supreme Arctic
1500 Mist
Control Stearate HT
Anti-load N/A 5.6 micron15 micron 7 micron 1.9 micron
Median
Particle
Size
Dry coat N/A 14.80 ~ 13.32 ~ 13.32 ~ 13.32
weight
(g/m2)
Filler N/A 90 81 81 81
volume
(Anti-
loading
Agent)
Binder N/A 9.05 11 11 11
volume
Cut 100% 136% 121 % 134% 137%
(% of Control)
Surface 0.46 0.41 0.46 0.46 0.46
Finish,
Ra
(gym)
Table 1
Vertal 1500, Supreme HT and Arctic Mist are talc's available from Luzenac
America,
Inc.
Example 2: Hydrous Magnesium Silicate (Talc~preme HT in different grit sizes
The following tables illustrate a comparison of grinding performance of
Supreme HT Talc with zinc stearate, and a control with no anti-loading agent
for an
aluminum oxide coated abrasives in grits P80, P180, and P320 (Table 2, Table
3,
and Table 4, respectively). The results show that the cut was higher with the
incorporation of anti-load agent of the present invention versus base control
especially in finer grits.
_g_
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
P80 Base Control Witco Zn-St Supreme HT Talc
Dispersion
Dry coat weightN/A 14.80 ~ 13.32
(g/m2)
Filler volume N/A 90 81
%
(Anti-loading
agent)
Binder volume N/A 9.05 11
%
Cumulative Cut 21.61 24.43 22.54
(g)
Cut of Control 100% 113% 104%
Ra 1.88 1.96 2.05
(pm)
Table 2
P180 Base Control Witco Zn-St Supreme HT Talc
Dispersion
Dry coat weightN/A 14.80 13.32
(9/m~)
Filler volume N/A 90 81
%
(Anti-loading
agent)
Binder volume N/A 9.05 11
%
Cumulative Cut 15.87 23.5 19.76
(g)
Cut of Control 100% 148% 125%
Ra 0.84 0.89 0.89
pm
Table 3
_g_
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
P320 Base Control Witco Zn-St Supreme HT Talc
Dispersion
Dry coat weightN/A 14.80 ~ 13.32
(g/m2)
Filler volume N/A 90 81
%
(Anti-loading
agent)
Binder volume N/A 9.05 11
Cumulative Cut 7.75 13.51 12.93
(g)
Cut of Control 100% 174% 167%
Ra 0.46 0.41 0.43
(pm)
Table 4
Example 3: Amorphous Silica, Calcium Silicate ~Wollastonite, , Aluminum
Silicate
Clays and Potassium Aluminum Silicate I,Mica~
A standard P320 grit A-weight paper aluminum oxide conventional coated
abrasive is used. To this base coated abrasive is applied an oversize coat
comprising an anti-load additive of either Amorphous Silica, Calcium Silicate
(Wollastonite), Aluminum Silicate (Clay) or Potassium Aluminum Silicate
(Mica).
The grinding results, set forth in Table 5 below, show that the cut was higher
with
the incorporation of anti-load agent of the present invention versus base
control.
-10-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
Anti-LoadNlA AmorphousCalcium AnhydrousHydrous Hydrous
Material Silica Silicate Aluminum AluminumPotassium
Silicate SilicateAluminum
(Clay) (Clay) Silicate
(Mica)
Item Control MN-23 WollastoniteOptiwhiteBurgess Mica 325
17
Dry coatN/A 4.44 51.80 7.40 16.28 2.96
weight
(g/m2)
Filler N/A 81 83 80 79 79
volume
(Anti-
Loading
agent)
Binder N/A 12 10 12 12 12
volume
% Cut 100% 161% 113% 179% 113% 149%
of
Control
SurFace 0.61 0.51 0.43 0.53 0.61 0.38
roughness,
Ra
(gym)
Table 5
MN-23 is amorphous silica available from Eagle Pitcher.
Wollastonite 325 is a calcium silicate available from NYCO Minerals, Inc.
Optiwhite is clay available from Burgess Pigment Company.
Burgess 17 is a clay available from Burgess Pigment Company.
Mica 325 a mica available from Oglebay Norton Specialty Minerals.
Example 4: Calcium Sulfate~anhydrous and hydrous)
A standard P320 grit A-weight paper aluminum oxide conventional coated
abrasive is used. To this base coated abrasive is applied an oversize coat
comprising an anti-load additive of Calcium Sulfate (anhydrous or hydrous).
The
-11-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
results, . set forth in Table 6 below, show that the cut was higher with the
incorporation of anti-load agent of the present invention versus base control.
Anti-Load Material Anhydrous CalciumHydrous Calcium
Sulfate Sulfate
Item Base Control SNOW WHITE TERRA ALBA
Dry coat weight N/A 34.04 29.60
(g/m2)
Filler volume N/A 76 82
%
(Anti-loading
I 0 agent)
Binder volume N/A 14 9
%
Cut of Control 100% 153% 141
Surface roughness,0.51 0.41 0.43
Ra (gym)
Table 6
SNOW WHITE is an anhydrous calcium sulfate available from United States
Gypsum Company.
?0 TERRA ALBA is a hydrous calcium sulfate available from United States Gypsum
Company.
Example 5: Water contact angle of sanded paint panels after sanded by with
?5 Primer panels were sanded with P320 grit coated abrasives with oversize
coating described in Examples 1 to 4. The same sanded procedure was used with
each coated abrasive. A drop of water was then placed on each of the freshly
ground panels and also on panel that had received no grinding and the contact
angle (8) as described in the Figure was recorded. The contact angle is the
angle
30 between the surface of a liquid and the surface of a solid plane at the
line of contact.
A higher contact angle is indicative of less wetting. The results are shown in
the
Table 7 which clearly indicates that the panel ground with a coated abrasive
-12-
CA 02432163 2003-06-19
WO 02/062531 PCT/USO1/49590
according to the present invention had essentially the same or lower contact
angle
as the panel ground using a coated abrasive without the anti-loading layer.
The
coated abrasive having the conventional zinc stearate anti-loading layer
clearly
deposited a low surface energy residue the presence of which is indicated by
the
very high water contact angle. The consequence of this is that paints applied
to
such a surface do not readily wet the surface and this leads to surface
defects.
Anti-Load N/A Zinc Hydrous Hydrous Calciu Anhydrou
Material StearateMagnesium Potassiumm s Calcium
Silicate Aluminum SilicateSulfate
(Talc) Silicate
(Mica)
Item Base Zinc Supreme Mica 325 WollastSNOW
ControlStearateHT -onite WHITE
Dry coat N/A 14.80 7.40-17.762.96 51.80 34.04
weight
(g/m2)
Filler volumeN/A 90 81 79 83 76
I 5 (Anti-loading
agent)
Binder NlA 9.05 11 12 10 14
volume
Water 115 140 114 119 86 107
!0 Contact
Angle
(degree)
Table 7
!5
The water contact angle on panel that had received no grinding is 69 degrees.
While this invention has been particularly shown and described with
references to preferred embodiments thereof, it will be understood by those
skilled
.0 in the art that various changes in form and details may be made therein
without
departing from the scope of the invention encompassed by the appended claims.
-13-
